As is well known in the spray coating technology the heretofore known spray application equipment for coating substrates with conventional high solids have transfer efficiencies that are less than 50% which results in excessive loss of materials, solvents and time. Of significance in this technology is the ecological standards that one must consider since the impact on the quantities of materials, solvents and volatile organic compounds that are released into the atmosphere are not only a major concern of the caring individuals but must comply with the Occupational Safety and Health Administration (OSHA) and the Environment Protection Agency (EPA) requirements. Moreover, the current conventional coating systems presents a myriad of problems including, but not limited to, safety to the operators, environmental hazards, high costs and difficulties encountered when attempting to apply the coating.
There has always been a need for a high solid coating system that would coat the substrate with solids that would be between 5-10 mils thick in one pass without the necessity of a solvent.
We have found that we can provide a uniquely designed spray apparatus and method of applying the spray to the substrate while obtaining substantially 100% solids. The convergent spray technique of this invention will not only obviate the problems alluded to in the above paragraph but will eliminate the use of hazardous materials that would otherwise be used. It is contemplated by this invention to use a forced air stream to introduce the dry metallic filler material into a wet resin stream where it is convergently combined with the resin components. This invention contemplates utilizing a spray nozzle and system that is similar to that disclosed in U.S. Pat. No. 5,565,241 granted on Oct. 15, 1996 to Mathias et al of which Jack G. Scarpa, is a common co-inventor, entitled "Convergent End-Effector" and U.S. Pat. No. 5,307,992 granted on May 3, 1994 to Hall et al of which Jack G. Scarpa is a common co-inventor, entitled "Method and System For Coating A Substrate With A Reinforced Resin Matrix" both of which are commonly assigned to USBI Co., and which are incorporated herein by reference. As stated in the U.S. Pat. Nos. 5,565,241 and 5,307,992 patents, supra, the apparatus for applying the coating of reinforced resins matrix to a substrate is a spray nozzle that includes a centrally disposed orifice and a plurality of circumferentially spaced orifice(s) surrounding the center orifice for creating an atomizing zone. Included are other orifices radially spaced outwardly from these orifices which are used for shaping the spray. Reinforcing material is introduced to the resin through the aft end of an encircling chamber or manifold that surrounds the spray nozzle and is designed to feed the reinforcing material to the liquid resin. Pneumatic eductor lines for conducting compressed air are utilized to transport the materials to the substrate.
The present invention modifies the circumferential air atomization cap of heretofore known spray nozzle to include a central orifice that measures approximately 0.187 in diameter and includes an atomization angle of 90.degree.. The filler is concentrated into two distinct streams thus eliminating the buildup of the material on the surfaces and crevices of the spray applicator and transfer lines. This will result in enhanced transfer efficiencies and a more consistent finish of the coating on the substrate surface. The method employed utilizes a hopper and gravity fed loss-in-weight feed system under control into an eductor manifold system that transports the filler material through two separate streams prior to arrival at the spray applicator. A constant dry filler to liquid resin ratio assures a consistently applied coating.
By controlling the amounts and rates of resin and dry metallic filler and the proper ratios for coating selected surfaces, the entire system delivers, meters and mixes these materials only on demand of the convergent applicator with a consequential elimination of the requirement to pre-mix the coating formulations. This convergent spraying technique for dry fillers and resins provide a uniform controllable coating and if desired, this invention contemplates the option of heating the separate resins (when two or more resins are utilized) so as to accelerate the gel times of the sprayed materials. This optional method enhances the coating since it allows for a uniform buildup of the coating.
This invention has been particularly efficacious for solventless application of MagRam type of coatings (stealth applications) and highly filled zinc or other metallic fillers for corrosion resistance.
The system and spray nozzle of this invention also provides the following improvements, although not limited thereto, over the heretofore known system:
This system is compatible with epoxy, polyurethane, silicate water base or 100% solid resin systems;
This system has the ability to more accurately control thickness of applied coating;
This system has the ability to control the dimensions of surface area to be coated;
This system has the ability to control both filler and resin material independently;
The system reduces the number of required passes to attain a desired thickness of the coating in contrast to solvent borne systems;
This system reduces waste and hazardous materials;
This system has the propensity of reducing of time required to apply coating, reducing the time to test MagRam properties of coatings, and reduces solvents (VOC's) to apply zinc rich coatings; and
This system optimizes the loading capabilities by allowing the loading to be between 0%--a high of over 90%. This is also dependent upon resin and atomization characteristics of resin compenents.